1. Field of the Invention
Diagnostic and therapeutic procedures of the type dependent upon immunoreaction of antibody with a target tissue are frequently hampered by both the immunogenicity of the reagent in clinical applications and binding to cell surface Fc receptors. Immune response to antibodies and other foreign proteins, characterized by both allergic phenomena and inactivation of the protein, must be countered by treatment of the protein to obviate stimulation of the host immune system while retaining desirable protein biologic activity. In addition, it is desirable to increase antibody specificity by reduction or elimination of Fc binding to cell surface receptors.
2. Statement of Related Art
A variety of protein-modifying procedures has been employed to decrease immunogenicity of foreign proteins. In particular, suppression of human immunologic response to foreign antibodies without destruction of antibody activity has been previously accomplished by enzymatic digestion of the antibody to cleave the Fc fragment of the molecule. The product fragments retain binding capacity for antigen and can be coupled with a variety of chemicals to provide complexes of low immunogenicity. Protease digestion of antibodies is, however, a slow process with low yields, requiring separation of the product fragments.
A more attractive approach has been the proposed chemical modification of antibodies to provide products having high antigen binding capacity, low immunogenicity, and substantially no toxicity. Such proposed modifications have been broadly based on the known immunoinhibitory effect of hydrophilic polymers such as polyethylene glycol (PEG) and polyvinyl alcohol (PVA) on therapeutically useful enzymes, cf: J. Biol. Chem. 252: 3578-3586 (1977); Biochim. Biophys. Acta 660: 293-298 (1981); Clin. Exp. Immunol.46: 649-652 (1981); Biochim. Biophys. Acta 578: 47-53 (1979); Int. Arch. Allergy Appl. Immunol. 56: 159-170 (1978); J. Immunol. 126: 407-413 (1981); and Int. Arch. Allergy Appl. Immunol. 63: 1-13 (1980). The reported modification procedures have not been generally applicable to antibodies, however. In an exemplary investigation, reported in Radioimmunoimaging and Radioimmunotherapy, Elsevier Science Publishing Co. New York, N.Y., 1983, a PEG 6000 derivative of rabbit antihuman serum albumin was prepared employing a cyanuric chloride coupling procedure successfully employed in the modification of albumin with PEG (J. Biol. Chem. 252: 3578-3581, 1977). While the product exhibited reduced immunogenicity, loss of avidity for antigen was unacceptable (nearly 70% reduction in binding capacity). A similar result was obtained in a related study J. Immunol. Methods, 59: 327 (1983), wherein it was concluded that PEG-modification of Ig mediated with cyanuric chloride destroyed antibody activity.